The subject matter disclosed herein relates to heaters, and more particularly to heaters used in air conditioning units.
Current air conditioning units such as package terminal heat pump (PTHP) units and package terminal air conditioner (PTAC) units are known to use a ceramic heater to provide electric heating within the unit. The ceramic heater in such units is known to have a positive temperature coefficient (PTC) of resistance, and is thus known as a PTC heater. The types of ceramics used in PTC heaters include, but are not limited to, barium titanate and lead titanate composites. The ceramic heater may be used for a room heating function (e.g., in the PTHP unit) and for a unit defrost function (e.g., in the PTAC unit).
While the PTC heater provides benefits such as lower wattage density and self-regulation, which are favorable for safety purposes, the PTC heater is susceptible to wattage degradation over the life of the heater. It has been proposed in the U.S. patent application entitled “Triac Control of Positive Temperature Coefficient (PTC) Heaters in Room Air Conditioners,” Ser. No. 12/704,816, filed Feb. 12, 2010, the disclosure of which is incorporated by reference herein, to slowly ramp up the heat output of a PTC heater, using a triac control methodology, to help minimize the wattage degradation effect over the life of the heater. This gradual heat up of the PTC heater, which can take up to several minutes to reach a full heat output level, may not be desirable to some users.